Light interrupting means for photo-electric control system



July 9, 1957 F. w, sEYBQLD ETAL 2,798,967

LIGHT INTERRUPTNG MEANS F' OR PHOTOELECTRIC CONTROL SYSTEM originalFiled Dec.. 9, 195o 3 sheets-sheet 1 16.7 A FIG 6 TTORNE YS' July 9,1957 F. w. sEYBoLD l-:TAL 2,798,967

LIGHT INTERRUPTING MEANS FOR PHOTOELECTRIC CONTROL SYSTEM Original FiledDec. 9, 1950 I .'5 Sheets-Sheet 2 IN VEN TORS July 9, 1957 F, w, SEYBOLDET AL 2,798,967

LIGHT INTERRUPTYING MEANS FOR PHOTOELECTRIC CONTROL. SYSTEM OriginalFiled Dec. 9, 1950 3 Sheets-Sheet 3 F'IG. i5

Unite LlGll-l'i {NTERRUPTNG MEANS FR PHT- ELECTRIC CN'IROL SYSTEM`Frederick W. Seyhold, Westfield, N. J., and Nicholas Herman, Bronx, N.Y., assignors to E. P. Lawson Co., Inc., New York, N. Y., a corporationof New Joris 3 crainte. (crassa-.234)

Our present invention is a division of application Serial No. 200,013filed December 9, 1950 now Patent #2,737,158, and relates to stop andtrip out units, electrical circuits for electrically controlledautomatic hydraulic spacing mechanism and more particularly to stop andtrim out units and electrical circuits for automatic spacing mechanismspeciiically designed for use in connection with guillotine type papercutters. Other patents showing mechanical elements of the machine suchas the back gauge, cable attachments, etc., and various features ofmachines suitable for use with the invention disclosed herein are shownin Patents #2,628,680; #2,053,499; #2,687,011; #2,574,501.

In the operation of guillotine type paper cutters, a pile of paper isplaced on the work table beneath the cutting knife. The back gaugeusually provided on the work table is then adjusted so that the portionof the pile which is desired to cut off extends forward of the cuttingknife edge so that when the knife is brought down, it will cut off anexactly dimensioned section of the pile.

In operating paper cutters of this type, therefore, it frequentlybecomes necessary to adjust the back gauge many times for different cutswhich are to be made. Even if a plurality of regular cuts are to be madefrom a single pile, the back gauge must be moved up each time in orderto ensure that the edges are perfectly squared so that the exact cut maybe made,

An object of our invention is the provision of a novel stop unit for aphoto-electric cell circuit that controls the automatic back gaugespacing mechanism which moves the back gauge at successive individuallypredetermined intervals after successive cuts.

By the use of our invention, therefore, the operator need do nothingmore than place the initial pile of paper on the machine against theback gauge and arrange a program of stop units. The operator thenoperates the paper cutter each time a signal lamp flashes so that theknife moves up and down the desired number of times to cut the desirednumber of piles.

A further object of our invention is to provide a signal light whichwill indicate to the operator that the back gauge has come to thepredetermined stop.

The program of stop units will control the spacing mechanism so that theback gauge driving mechanism automatically moves the back gauge theproper distance at the end of each cut and before the next cut isstarted.

Our invention is directed specifically to stop units and electricalcircuits. The stop units interrupt a light beam and thus permit theelectrical circuit to `exercise proper control of the electricallycontrolled elements for successively moving the back gauge bypredetermined intervals after individual cuts.

The stop and trim out units are used in conjunction with a carriagemoving transversely across the front of the cutting machine insynchronism with the movement States Paten-t rice of the back gauge andmoves with a speed equal to that of the back gauge.

A photo-sensitive medium, such as a photo-electric tube, and a lightsource are borne by the carriage across the front of the machine and astationary program of stop units is located between the light source andthe photo-sensitive medium.

A hydraulic driving mechanism is provided for the back gauge and iscontrolled by the novel electrical circuits of our invention. Theelectrical circuits are switched on and olf to control the drivingmechanism by the manner in which light falls on the photo-sensitivemedium as determined by the program of stop units.

ln its simplest form, the stop units are rectangular members, thelefthand edges of which are each spaced from each other by the exactdistance which the back gauge is to travel between successive cuts.

In another form, the program of stop units can be reproduced andreplaced by a transparent regulating strip v/hich is provided with aplurality of successive rectangular opaque sections, the left-hand edgesof which also may be spaced from each other by the exact distance whichthe back gauge is to travel between successive cuts.

When the operation of the back gauge is initiated, a light beam passesin the space between stop units or through the rectangular transparentarea of the regulating strip. This operation takes place at full speedto drive the back gauge forward rapidly. At the same time, the carriageis driven transversely from right to left at equal speed through cableattachments to the back gauge.

When light from the light source is first interrupted by the right-handedge of the stop unit or the right-hand edge of the opaque section `inthe regulating strip, cir* cuits are operated to reduce the forwardspeed of the back gauge and the carriage to a slow speed.

When the light from the light source is again permitted to impinge uponthe photo-electric cell by the left-hand edge, a heavy pile of paper maybe brought up rapidly by the back gauge to near the point where it is tobe stopped. Thereafter, it is slowed down and then finally brought to astop. The slow-down interval prevents a sudden stop of the back gaugefrom causing a paper pile to cross beyond the predetermined position.

Thus, the linal speed of the back gauge and its carriage may be aslittle as 1% of the speed at which the paper pile is brought up close tothe stopping point.

Thus, the width of the rectangular stop units depends on the rapiditywith which the electric relays, solenoids, and valves respond to thelight signals to slow down the paper pile sufficiently so that it willbe stopped accurately.

Preferably, the initiation of the back gauge operation is so arrangedthat the lifting of the knife and clamp clear of the paper pile will setthe apparatus in motion by means of a knife switch, although a by-passswitch may be provided so that the back gauge may be set in motionmanually when desired.

The primary object of our invention is the provision of a novelconstruction and adjustment of stop units set between a photo-sensitivemedium and a light source which moves synchronously with the back gaugeto alternately interrupt and permit passage of the light beam atpredetermined positions of the back gauge. The control elements are soarranged that the first change in the light conditions due to theright-hand edge of the stop unit after Vthe initiation of fast operationwill cause the back gauge to be slowed down and the second change in thelight condition due to the left-hand edge of the stop unit afterinitiation of the operation will cause the back gauge to be stopped.That is, the darkening of the photo-sensitive medium will cause a slowdown and the relighting of the photo-sensitive medium will cause thehydraulic means to stop the back gauge.

When the cutting machine is called upon to cut labels or other materialprinted upon the sheets of the pile of paper, the back gauge is requiredto move forward an inch or more between each cutting operation. However,on printed sheets where many rows of labels or the like appear, there isalso found a small strip of between M6" to E" which is unprinted. Theseunprinted strips are due to the plate hooks which are located betweenadjacent printing plates to clamp these plates to the printing cylinderas is well-known in the art. Hence, after the back gauge has been movedforward several cycles of fast and slow speed to cut a series of printedlabel rows, it becomes necessary that the back gauge move forward only afraction of an inch to permit the cutting of the small unprinted strips.Therefore, it is necessary that the back gauge start to move forward ata slow speed and then come to a stop.

For this purpose a time delay relay is incorporated in the electriccircuit whereby the back gauge moves forward at slow speed for afraction of a second so that the photo-sensitive medium will be darkenedin case the next adjacent stop unit is only -a short distance from thepreceding one before the hydraulic means is conditioned for fast forwardspeed. If the back gauge were to start moving forward at a fast speed,the inert-ia of the system would not permit it to stop accurately aftera fractional inch of travel and thus the cutting operation would nottake place at the proper location on the pile of paper.

For the purpose of trimming out these small strips of unprinted paper, aspecial light beam interrupting unit is provided. This special means iscalled a trim out unit which controls the back gauge movement in such amanner that it will start to move forward from a stopped position at aslow speed, travel the fract-ional inch of the unprinted strip and thencome to a stop.

Another object of our invention is a novel construction and adjustmentof a trim out unit to be used with the heretofore mentioned stop units.The trim out unit is placed to the left of a stop unit so that thedistance between the right edge of the former and the left edge of thelatter forms a narrow slit.

Our invention is used in conjunction with a novel electrical c-ircuit inwhich a time delay relay is incorporated to function in coordinationwith trim out units to permit trim out operation at slow speed, asdisclosed in aforementioned Patent No. 2,737,158.

The movement of the back gauge is described in detail in Patent No.2,737,158 in coordination with the carriage which carries thephoto-electric unit, a description of the general operation and coactionbeing now given.

The carriage is to the right of the stop unit, as viewed by an operatorfacing the front of the machine. Full light impinges upon thephoto-electric cell so that after a cutting operation is completedupward movement of the knife blade will initiate slow speed for afraction of a second to be followed by fast forward movement of the backgauge. Due to the cable attachment between the back gauge and carriage,the carriage will move to the left and when it reaches the right-handedge of the stop unit, the light beam will be interrupted by the stopunit to cause the back gauge to now move forward at a slow speed. As theback gauge continues to move slowly forward and the carriage reaches theleft-hand edge of the stop unit, the light beam will again be permittedto impinge upon the photo-electric cell and thus cause the hydraulicsystem to bring the back gauge to an accurate stop.

Assuming that a trim out unit is adjacent the stop unit, a slit of onlya fractional inch will exist between these two units through which thelight beam will pass. If a green light signal has tiashed, indicatingthat an accurate stop has been made, the operator can then start Cil thecutting operation. When the knife blade on its return upward movementcloses the knife switch, it will initiate slow speed of the back gaugefor a fraction of a second. However, within this fractional secondperiod, the carriage will reach the right-hand edge of the trim out andthe light beam will again be interrupted. As heretofore noted, this willpermit the back gauge to continue to advance at a slow speed until thelight beam and carriage reach the left-hand edge of the trim out unit.At this point, the light beam again permitted to impinge upon thephoto-electric cell and will cause the electrically controlled hydraulicdriving mechanism to bring the back gauge to a stop. If the green signallight indicates that an accurate stop has been made, the cuttingoperation can take place to trim out the strip of unprinted paper. Sincethe carriage comes to a stop at the left-hand edge of the trim out unitwhere light can impinge upon the photo-electric cell, the electricalcircuit is in condition to cause the hydraulic driving mechanism to movethe back gauge forward as described bcfore.

The stop units and more particularly the trim out units must oe properlyadjusted individually in accordance with the desired spaced cuttingoperations required. In addition, these units must be adjusted andpositioned with respect to each other and thus a combination membercontaining both a stop unit and a trim out unit is provided.

Our invention provides a novel blocking member and control which ismounted yand controlled from the carriage and is used for positioningthe stops on the hexagonal bar relative to the photo-sensitive mediumwhich is attached to the carriage. The back gauge and carriage are movedto the predetermined cutting location, and the blocking member ismanually moved in the path of the units. A unit is then moved along thestationary hexagonal bar until it engages the blocking member. Thislocation of the unit on the hexagonal bar will then be in properpredetermined position relative to the phototube -and it may then besecurely fastened to the bar at this point.

Accordingly, another object of our invention is to provide a blockingmember and control so that the stop unit may be positioned properly onthe hexagonal bar so that a program of stop units may be arranged toresult in the required spaced movements of the back g-auge.

The foregoing and many other objects of our invention will becomeapparent in the following description and drawings in which:

Fig. l is a stctional view showing the relationship of the photo-cell,light source, and stop unit.

Figure 2A is a side view of a novel combination stop unit and trim outunit of our invention.

Figures 2B and 2C are side views of another novel combination stop unitof our invention. Figure 2B shows the trim out unit adjusted for maximumtrim out and Figure 2C for minimum trim out.

Figure 3A is a bottom view of the novel combination stop unit of Figure2A.

Figures 3B and 3C are bottom views of the novel combination stop unit ofFigures 2B and 2C.

Figure 4 is a perspective view of Figures 3B and 3C showing the hingeconstruction of the trim out unit.

Figure 5 is a top view of a novel combination stop unit of our inventionshowing the adjustment means for the trim out unit.

Figure 6 is a front view of the novel combination stop unit of Figure 5.

Figure 7 is a View taken along section 7-7 of Figure 6.

Figure 8 is a front View of another novel combination stop unit of ourinvention.

Figure 9 is an end view taken along line 9--9 of Figure 8.

Figure 10 is a view taken along line lll-10 of Figure 8 showing the trimout unit in open position.

Figure 11 is a view similar to Figure 10 showing the hinges' of the trimout unitn closedposition.

Figure 12 is a perspective view of the trim out unit of Figures 10 and1l showing the links and construction.

Figures 13, 14 and 15 are a top, front and end view respectively, of anovel modified combination stop vunit of our invention.

Referring to Fig. l, a photo-tube 360 and light source 359 are supportedon carriage 63 whichv moves in synchronization with a back gauge, all asdescribed in our prior Patent No. 2,737,158.

The carriage 63 travels along the bar 64 due to the motion imparted toit by the cables as lheretofore described in the aforementioned patent.That is, the movement of the back gauge is duplicated by the carriage 63so that when the back gauge is all the way back, the carriage 63 is allthe way to the right and as the back gauge moves forward, the carriage63 will move to the left. The carriage 63 carries the housing 364 inwhich is mounted a light source 359. A slit 365 in the housing 364permits the light from' source 359 to travel directly to aphoto-electric cell 360. The photo-electric cell 360 is mountedhorizontally in the housing 361 which in turn is rigidly attached to thecarriage 63.

The photo-electric cell is either illuminated or dark and the changefrom one to the other is responsible for the control of the hydraulicsystem. Preferably, the photo-electric cell 360 is illuminated when theback gauge is travelling at high speed. When this illumination isinterrupted by a signal unit and the photo-electricv cell is dark, thephoto-electric will cause the electric circuit to slow down thehydraulic motor. When the photoelectric cell is again illuminated, itwill cause the hydraulic motor to stop.

First Stop unit One type of stop unit is illustrated in Figures 2A and3A as stop unit 365. L-shaped stop unit 365 has a long leg 365e and ashort leg 365d which is provided with a tongue 366 which iits into thedove tail groove 367 and properly aligns the stop as seen in Figure 1.The stop unit 365 is clamped to the hexagonal bar 376 by means of screw369 and wedge-shaped nuts 370 as may best be seen in Figure l. Theright-hand edge 365a of leg 365e serves to interrupt the light beam whenthe carriage 63 is at a predetermined location.

When the carriage 63 is at the right of the stop unit 365, there will beno obstruction to the beam of light from source 359 and the back gaugewill be moving forward at high speed. As the carriage continues to moveto the left, the beam of light will be interrupted by the right-handvertical edge 3:65a.

Thus, the photo-electric cell 360 will be darkened and by means ofamplifier tubes and relays will cause the electrically controlleddriving member to change to a slow speed. Since the back gauge istravelling at a linear speed of about seven inches per second, and anappreciable amount of time is required for the relays and drive memberto respond to this signal, the carriage 63 will travel about 75,-90% ofthe width of the stop unit 365e before the back gauge motor and backgauge assume a slow speed. As the carriagev 63 travels past theleft-hand vertical edge 365b, the stop `unit 365C again permits the beamof light to reach the photo-electric cell 360 will .cause the back gaugeto come to a stop. However, after the photo-electric cell 360 hasreceived this second signal, the back gauge and carriage 63 will travela certain distance beyond the left-hand edge 365b before coming to acomplete halt. This is due primarily to the inertia of the system.

Introduction to trmouts In the process of printing a sheet of labels onwhich many rows of labels appear, there will also be found strips and onthis signal the photo-electric cell circuit 6 ofWunpr-inted portions ofpaper. These-strips` are due to thefsp'ace between adjacentprintingplates which must be allowedV between these plates to place -theplate hooks which clamp the plates to the printing cylinder or base.

Thus, after a cutting operation when the back gauge need only moveforward a fraction of an inch to cut these unprinted strips, it becomesnecessary that the back gauge move :forward only in a slow speed.

As heretofore mentioned, after the second signal has been received, thecarrage'63 travels a short distance beyond the stop edge 36,511 beforecoming to a complete stop. Therefore, if another stop unit is placed atthe left of stop unit 365, there will remain only a narrow slit or spacefor the light beam to pass between the two stops. Thus, as thephoto-electric cell 360 received the second signal at edge 365'b, itwill travel past this edge a small amount before the back gauge 201comes to a stop. Hence, when forward movement of the back gauge is againinitiated, the carriage 63 will reach the righthand edge of the trim out385 before the timer mechanism 586 has closed its contacts. Hence, ashereinbefore described, the back gauge will continue forward at a slowspeed and permit a trim out cut to be made'when it comes to a stop atthe left-hand edge of trim out unit 385.

Since the trim out may be as small as 1/16 or as large as 5A" twoadjustable trim out units 371 and 372 are provided. The trim out unit371 is suitable for widths of i716 to 3A", while trim out unit 372 issuitable for widths of l/ev to SAG".

Figs. 2A and 3A show elevation and plan views respectively of trim-outunit 372, in light-transmitting position. The trim-out unit 371 is shownin elevation in light-blocking position in Fig. 2B and inlight-transmitting position in Fig. 2C. Figs. 3B and3C are plan views ofthe positions shown respectively in Figs. 2B and 2C.

Y Referring to Figures 2B, 2C, 3B, 3C, and 4, the trim out unit 371 hasa base 373 from which a thin rectangular leg 374 projects. A screw 375connects the stopunit 371 by means of base 373 to the hexagonal bar 376iu a manner heretofore described. The hinge 377 is rigidly attached tothe rectangular leg 374.' The other leg 380 of hingev 377 is rotatableabout the pin 378. The base 373 has an elongated slot 381 cut thereinand the attachment screw 375 passes through this slot.

The stop unit 371 thus has three degrees of adjustment (l) it may belocated by the screw 375 at any location in the slot 367 (Fig. 1) of thehexagonal bar 376; (2) the hinge 377 may be opened or closed todetermine the length of time that the photo-electric cell 360 will bedark to permit slow speed of the drive member. j

Thus, in the hinge open position of Figures 2B and 3B it would produce aslow forwardA movement of the back gauge of 1%" whereas the hinge closedposition of Figures 2C and 3C will give only a 9%16" forward movement;(3) due to the length of slot 381, the base of the stop unit 371 can berotated and still maintain the outer edge o-f the hinge 377 in alignmentwith the edge 365b of stop 365. This rotation of the base 373 permitsthe adjustment of the slot or space between the two units 365 and 371 asmay best be seen-*by comparing Figures 3B and 3C or Figures 2B and 2C.

Second trim out For very small widths of l/l to 3/16 the trim out unit372 is used as may be observed in Figures 2A and 3A. The base 382 isconnected to hexagonal bar 376 by the bolt 386 in a manner heretoforeexplained and 'has a thin short rectangular leg 383 projectingtherefrom. The short hinge leg 384 is rigidly attached to thisrectangular leg 383 while the longer leg 385 is adjustable for theinterruption of the light beam.

Introduction to combination The two trim outs 371 and 372 each have asmall 7 hinge which may be opened or closed depending upon the width ofthe narrow unprinted strip of paper which is to be cut or trimmed outfrom the printed paper. However, since these trim out units must beadjusted to rather close limits, it is desirable to provide a morepositive and more practical method of adjustment.

In addition to a trim out unit with an accurate and precise adjustment,it is also desirable to combine this with a stop unit as an integralmember thus alleviating some of the positioning problems involved.

First combination One trim out stop combination unit is illustrated inFigures 5, 6 and 7. The base 388 is secured to the hexagonal bar 376 bymeans of screw 387 in a manner heretofore explained. To this base 388 isfastened the short leg 389 of a standard stop unit by means of screws391. The long leg 392 of the standard stop unit interrupts the lightbeam as best seen in Figure 6.

An adjustment screw 393 is journalled in the base 388 and leg 389. A nut394 with a stem 395 is threaded on the adjustment screw 393. A stem 396projects downwardly and at its upper end is rigidly attached to the base388. A hinge 397 is tted over the stems 395 and 396 as is best seen inFigure 7. An adjustment shaft 398 is journalled in the base 388 and itsend is fastened to a mitre gear 399 which meshes with a similar mitregear 400 fastened to the screw 393. At the other end of the adjustmentshaft 398 is located the knob 401.

Thus, when the knob 401 is turned, the adjustment shaft 398 by means ofmitre gears 399 and 400 will cause the adjustment screw 393 to rotate.This will cause the guided nut 394 to move along the axis of screw 393and thus open or close the hinge 397 depending on the direction ofrotation of knob 401.

The position of the part of the solid lines of Figure indicates the openposition of the hinge 396 when it interrupts the light beam for thelongest period of time. The dotted lines of Figure 5 and the position ofFigures 6 and 7 show the hinge in closed position when it interrupts thebeam of light for the least period of time.

Second combination unit A second design for the adjustable combinationof a standard stop unit and a trim out stop unit is illustrated inFigures 8, 9, l0, 1l, and 12. This combination unit is constructed asfollows: The base 404 is connected to the hexagonal bar 376 by the screw402 in a manner heretofore explained. The standard stop unit 426 isattached to the right of this base 404 by the screw 427. At the left ofthe base 404 is mounted the trim out stop unit. A pin 420 isperpendicular-ly mounted and rigidly attached to the base 404. A guidegroove 423 is provided in this base unit 404 and has the cylindricalguide pin 422 located within. An extension pin 421 extends verticallydown from the cylindrical guide 422. l

Pivotally mounted on this pin 421 are the two members 428 and 429. Themember 428 is pivotally mounted at its other end on the extension pin420. The blades 424 and 425 are rigidly attached to the lower side ofthe members 428 and 429, respectively, and form the hinge of a trim outunit. Hence it will be observed that when the extension 430 of member429 is moved down as viewed in Figure 10, the blades 424 and 425 willmove to a closed position as seen in Figure ll.

For this purpose of controlling the position of the blades 424 and 425,the adjustment screw 431 is provided. This adjustment screw 431 isconfined in the body 404 by means of the retaining plate 405. A nut 418is threaded on the screw 431 and rides in groove 432 of the base 404. Apin 419 projects from the nut 418 and is the pivot for the extension 430of member 429.

The hinges 424 and 425 of this trim out unit may thus be opened andclosed as follows: If the hinge is in the position of Figure l0 and thehead 403 of the adjustment screw 431 is turned in the proper direction,the nut 418 75 Third combination unit The combination unit of Figures13, 14, and l5 is designed for trim out as small as I1/16". In this unitthe base 433 is attached to the hexagonal bar 376 in the same manner asheretofore described.

A standard stop unit 434 is attached to the base 433 by means of screws435 and 436. An adjustment screw 437 is journalled in the base 433 andthe stop unit 434. A mit 438 with a pin 440 perpendicularly and rigidlyattached thereto is threaded on the screw 437 and is guided in thegroove 439 of the base 433. In slot 441 of the base 433 is a guide 442from which a second pin 443 is perpendicularly and rigidly attached.

A member 449 is pivotally mounted at its ends on these pins 440 and 443.The blade 444 is rigidly mounted on the lower side lof the member 449 ina slot located therein.

` As seen in Figure 13, if the nut 433 is caused to move to the right,the right end of member 449 will be guided down by the pin 443 and guide442. This will thus alter the angle of the blade and, therefore, alterthe trim out dimensions. Control of the nut 438 is accomplished by bevelgears 445 and 446, shaft 447 and head 44S. The shaft 447 is mounted inthe base 433 and is terminated at one end on head 448 and at the otherend in bevel gear 446. The adjustment screw 437 is also terminated atone end with a rigidly attached bevel gear 445 that is in meshengagement with bevel gear 446.

Hence, when the head 44S is turned, by hand or screw driver, the shaft447 will rotate and translate rotation to adjustment screw 437 by meansof bevel gears 446 and 445. Hence, if the head 448 is rotated in onedirection, the nut 438 will be found to move along the axis of screw437. Hence, when the nut 438 is in the extreme right position, the blade444 will be perpendicular to the screw 437 and will produce the shortestpossible trim cut movement of the back gauge.

Positioning 0f stop zmits Thus far we have described the purpose,construction and adjustment of the trim out and stop units. However,these units must be properly located on the hexagonal bar 376 before thecutting machine can be put in operation. Means are provided wherebythese trim out and stop units can be properly positioned on thehexagonal bar 376, as fully disclosed in our Patent No. 2,737,158 and asgenerally described hereinafter.

The back gauge and carriage are moved to a position where it is desiredto cut the paper stack. At this point a blocking member is interposed inthe plane of the stop unit. The holding screw 369 and its associatedwedge nut 370 are loose to permit the operator to slide the stop unitalong the dovetail groove 367. When the stop unit is moved along thegroove 367 to the point Where it engages the blocking member, theoperator will know that it is properly placed and can thus lock the stopunit in place by means of screw 369 and wedge nut 370.

One phase of our invention concerns itself with the blocking member andhow it is placed in the plane of the stop unit as will now be described.

First positioning As may best be seen in Figure l, a cylindrical bore465 is provided in the carriage 63 and a hollow cylindrical tube 450 isfitted therein. Thus, tube 450 has diametrically located slots 452 topermit pin 451 to enter therethrough. The pin 451 is rigidly attached tothe carriage 63 so that the slots 452 limit the upward and downwardmovement of the tube 450. A flanged portion 466 on tube 450 is alsoprovided to limit the downward travel of tube 450 by engagement withsurface 467 of carriage 63.

The blocking member 454 is pivoted on pin 449. The blocking member 454is biased downward against the tube 450 and thus out of the path ofthestop units.

When the operator wishes to place the blocking member in the path of thestop units so that these units can be set, the knurled head 456 of tube450 is pushed upward. Since this head 456 is an integral part of thetube 450, it will also move up, pushing the blocking unit 454 clockwiseagainst the bias of spring 453 t the position of Figure 1. The stop unit365 can now be brought into contact with the blocking member 454 andlocked in place on the hexagonal bar 376 by means of screw 369 and Wedgenut 370.

After the stop unit 365 is properly placed, the knob 456 is released topermit the tube 450 and blocking member 454 to return to the positionwherein the stop unit 365 is free to move past the blocking member 454and thus other stop units can then be positioned.

Since many Variations and modifications of our invention will now beobvious to those skilled in the art, we prefer to be bound not by thespecific disclosures herein contained but only by the appended claims.

We claim:

1. A photoelectric system for controlling start and stop positions of amovable element in a machine, comprising a light source and aphotoelectric cell for receiving a beam of light from said light source,said photoelectric cell and said light source being movable as a unit insynchronization with said movable element, means for interrupting saidbeam comprising a rst light interrupting member, means for positioningsaid member at selected points along the path of traverse `of said beam,a second light interrupting means adjacent said rst interrupting memberand spaced therefrom and comprising a rotative plate adjustablyrotatable with respect to said beam, including means for spacing saidlight interrupting members bodily with respect to each other.

2. A photoelectric system as set forth in claim 1 comprising anadditional plate to which said first-mentioned rotative plate ispivotally attached and means for adjusting said additional plate withrespect to said rst light interrupting member.

3. A photoelectric system as set forth in claim 2, said latter meanscomprising a base member, said rotative plate and said additional platebeing carried thereby, said base member being rotatively adjustable withrespect to said irst light interrupting member.

References Cited inthe tile of this patent UNITED STATES PATENTS1,901,677 Taylor Mar. 14, 1933 2,053,499 Seybold et al Sept. 8, 19362,215,211 Devol Sept. 17, 1940 2,438,098 Tandler et al. Mar. 16, 19482,557,691 Rieber June 19, 1951 2,604,597 Cahusac et al. July 22, 19522,628,680 Seybold Feb. 17, 1953 2,649,155 Spiller Aug. 18, 19532,665,388 Bickley Ian. 5, 1954

